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Old Jun 02, 2015, 11:39 PM
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Apprentice 15e rebuild, Cessna inspired

I picked up a second Apprentice 15e (no SAFE) for cheap on Craigslist, which had seen better days. The plane was filthy, had a bent motor shaft, busted cowl, busted wheels, and the tail feathers were warped. However, it was complete and included the transmitter, so I decided it would make a good project.

I made a custom horizontal and vertical stabilizer out of foam board from hobby lobby, both based on the Cessna 172. I left the paper on the foamboard, and coated both sides with a couple coats of polycrylic. This stiffened them up quite a bit, and also gave them a nice semi-gloss finish. The wires for the tail lights run down the leading edge of the fin, and have a strip of paper folded over them, which is also coated in polycrylic. For the rear white light, I poked a hole through the rudder and fin using a coat hanger, and fished the wire through it to the leading edge. The horizontal stabilizer and elevator each have a CF rod glued to the bottom to stiffen them up.

The wheels are Du-Bro Lite Flite 2.5". Lite Flites are my favorite wheel because they look good, are wide enough for grass use, and are super light. I switched out the nose gear for an S model one, to accomodate the larger nose wheel. It has the bend higher than the older model one.

I added slotted flaps, using Robart pin hinges. After adding flaps to my first Apprentice, I decided to do this one as well, it makes landing really easy. I cut them using a hot-wire cutter, following a straight-edge taped to the top and bottom of the wing. This allowed me to get a nice straight cut, and also a consistent bevel.

I've had crappy luck with painting foam, so the graphics on this are all cut out by hand from vinyl. The black pin stripe is automotive pin stripe from Autozone. The tail number was the hardest part - I found a font I liked online, and printed out the number to size on a sheet of paper. I then ironed the paper to the vinyl backing, which gets it to stick in place. Then, very carefully I cut out the letters using scissors and a hobby knife for the inside bits. The lines on the control surfaces were made simply with a pencil and straight-edge.

The light kit is custom code I wrote, running on an ATTiny85 microchip. There are red, green, and white position lights, a beacon on the tail (fades in and out to simulate rotating), and strobe lights on the wingtips. The landing light is controlled by the flaps channel - with flaps down, the light comes on. I had a derp moment and put the light on the wrong side, a C172 actually has it on the left wing. But I didn't realize it until I had already cut the foam, and decided it was fine. I will get a video of the lights soon, it really looks neat in the dark.

I hope you guys like it, and hopefully I can maiden it soon. I plan on giving it to my dad for father's day. He's always seems really interested in my other apprentice, but won't fly it for fear of crashing it. I figure if he has his own plane, maybe he won't have to worry about crashing my plane. Plus with the extra DX5e transmitter, I can buddy box off my DX8 and hopefully have no crashes at all.

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Last edited by Ward; Jun 02, 2015 at 11:45 PM.
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Old Jun 03, 2015, 09:10 AM
SantiColomo is offline
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That looks really cool. Looking forward to see the flying video. If possible I would like to see the lights at night time.
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Old Jun 03, 2015, 08:44 PM
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Well, I maidened it this evening. Turned out to be way tail heavy and nearly uncontrollable. Whenever I slowed down it would pitch up madly and stall. I wound up putting it in a tree trying to get it back on the ground, but no damage. I think I actually lucked out, the tree caught it pretty gently, and I'd much rather have that than a cartwheel landing. I apparently picked the tree with the most amount of tree sap all over it though, so I was a sticky mess after this. I am going to try a larger battery to get the CG forward - this was with the stock 3s 3200.

Apprentice 15e retrieval (0 min 19 sec)


Edit: Well, after cleaning the mud and tree sap off, she's as good as new. I tested CG with a Venom 3S 5000 pack, and it balances much better. I also found another reason why it flew so badly. After reviewing the onboard video, my wing rubber bands weren't strong enough, and the wing actually lifted off the fuselage several times in flight. This caused it to pitch up wildly and stall. I guess some new rubber bands are in order.

Apprentice 15e maiden (4 min 10 sec)


I did get some video of the lights at night, they're still working fine after the tree impact:

RC lighting system on Apprentice (0 min 17 sec)
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Last edited by Ward; Jun 03, 2015 at 10:27 PM.
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Old Jun 06, 2015, 09:15 AM
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Cool, I love the lights set up. I have no idea about lights. Do you think you could put a link to some similar kits to the one you are using?
I have to say you are so lucky the plane only ended up softly in that tree. That's the scariest video I've seen. It looks like you are only using 2 rubber bands?? If that's the case the instructions say you have to use 8. I take care of putting mines properly before I flight. Some times the wing goes a little bit off to one side and you can already feel like the plane wants to drift side ways, so having the wing strongly attached is a must.
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Old Jun 08, 2015, 01:59 PM
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I used four rubber bands, which felt tight enough on the ground, but I underestimated how hard the wing could pull. After rebalancing the plane, I use 8, and it's been perfect.

I don't know of a similar light kit, which is partly why I built my own. Horizon sells a simple one here:
http://www.horizonhobby.com/controll...ht-kit-efla600

But the on/off toggles all of the lights, not just the landing light. It also doesn't blink or strobe. I did publish my code on Github, and if you're familiar with arduino it's pretty easy to build. I used an ATTiny85 chip in order to keep it small, but any arduino board would also work:

https://github.com/hasbridge/arduino-rc-nav-led
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Old Jun 11, 2015, 12:16 PM
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Hey that looks like the park by my house!
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Old Jun 12, 2015, 10:36 AM
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Quote:
Originally Posted by mu5tanggt View Post
Hey that looks like the park by my house!
Well there can't be too many parks with an M41 Bulldog parked in them :P
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